Solid-liquid interfaces are the site of many types of chemical and physico-chemical reactions. In particular, the interfaces between conductive solids (especially metals) and electrolytes are the site of electrochemical reactions that have many possible applications: generation and storage of electrical power, production of chemical and biochemical sensors, catalysis, etc.
These reactions are complex phenomena, involving a number of steps, which are particularly difficult to understand and control. Because of this complexity, studies carried out in this field mainly focus on planar surfaces; likewise, planar surfaces are preponderantly used in practical applications. With the gradual integration of complex analytical devices, it is increasingly important to take into account the local character of electrochemical phenomena. Furthermore, the study in real time of reaction kinetics provides essential information on these mechanisms. For these reasons there is an increasing need for tools combining local electrochemical measurements and imaging. The simplest imaging techniques are optical techniques; unfortunately, it is difficult to combine them with local electrochemical measurements. Specifically, electrochemical reactions occur on the surface of electrodes, which are generally opaque, making contact with an electrolyte; therefore, in accordance with the prior art, an optical imaging device used to study such a reaction must be arranged in the half-space containing the active surface of the electrode and the electrolyte. However, the local electrochemical measurements must also be carried out in the same half-space, for example by means of a scanning contact probe that scans the electrode; such a probe may get between the optical imaging device and the surface, hindering observation of the latter.
Even in the absence of these blocking constraints, the observation of a surface through an electrolyte may prove to be difficult. Moreover, the modifications of the surface of the electrode that are induced by an electrochemical reaction often have a low optical contrast—think for example of the very first stages of deposition of an electrolytic layer, when said layer has an average thickness of about one nanometer or less.